Low temperature refrigeration system for cascade operation



P. H. BRANDT July 17, 1956 LOW TEMPERATURE REFRIGERATION SYSTEM FOR CASCADE OPERATION Filed Sept. 20, 1952 w 4 a i 2 1% W w M/ 5 w a A T v //E fi .7 Mm M w m Lfi w; a m mma 1m, 2.? 401.. M a n i HIGH mmw A??? j.

LOW TEMPERATURE REFRIGERATION SYSTEM FOR CASCADE OPERATION Paul H. Brandt, Park Ridge, Ill., assignor to Murphy & li iiller, Inc, Chicago, 111., a corporation of Illinois Application September 20, 1952, Serial No. 310,689

3 Claims. (Cl. 62117.6)

My invention relates to an improved low temperature refrigeration system for cascade operation and particularly relates to an improved mechanism whereby flow of refrigerant to the low temperature evaporator is controlled in a positive manner without interfering with the safety contrOls which prevent overloading the low temperature system when operation of the unit is initiated.

Cascaded refrigeration systems use a pair of conventional refrigeration systems with the evaporator of one system (the high temperature system) forming the cooler for the other (the low temperature system). Each refrigerant and system is then required to cool over only part of the total temperature range of the combined system, thus making possible a greater elfective range of temperature drop than can be obtained by the use of a single system and refrigerant. In systems of this kind it is very important to provide safety shut-off controls to avoid operation of the low temperature system until the cooler of that system is brought down to nearly normal operating temperature. Unless this control is provided, the low temperature unit may start operation before the cooler is down to operating temperature and the low temperature system accordingly is overloaded.

The apparatus of the present invention, a high pressure float valve mechanism, is used to control the discharge of liquid refrigerant from the low temperature cooler to the low temperature evaporator. A mechanism of this type has heretofore been subject to the disadvantage, however, of being subject to vapor locking in the closed position, thus preventing flow of the refrigerant and preventing any cooling action. In the apparatus of the present invention this action is precluded by the provision of a discharge path for vaporized refrigerant from the float valve to the cooler. As so constructed the low temperature system is effective in operation and can be used with high pressure safety devices to prevent operation of the low temperature system until operating temperature is reached.

it is, therefore, a general object of the present invention to provide an improved low temperature system for a cascade type refrigerator.

Another object of the present invention is to provide an improved low temperature refrigerator system which can be provided with a simple high pressure cutout to protect it against overload.

Still another object of the present invention is to provide an improved refrigeration system suitable for cascade operation and wherein a high pressure float control is provided in a manner that prevents vapor locking action.

The novel features of the present invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation and as to further features and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

Figure 1 is a side-elevational view with parts in cross section and in diagrammatic form showing one cascade nited States Patent 2 refrigerator system constructed in accordance with the present invention; and

Figure 2 is a cross-sectional view through the well portion of the cooler of a modified embodiment of the invention; and

Figure 3 is a greatly enlarged fragmentary portion of Figure 1.

Referring now to Figure 1, there is shown at 10 a refrigerator compressor driven by electric motor 12. The discharge pipe 1 of this compressor extends to the high temperature cooler 16 and thence, through line 14a, to the dehydrator 18. The line continues from dehydrator 18 to the expansion valve 20, as indicated at 14b. Refrigerant in the system passes through the minute orifice of the expansion valve 29 to discharge into the line or pipe 22. and thence into the inner tube 24 of the heat exchanger 26. This inner tube 24 extends in a serpentine path in the exchanger 26 and communicates with the suction line 28 leading to the compressor 16.

The system above described forms the high temperature portion of the mechanism of the present invention. The system is charged with a suitable refrigerant, such as Freon 22, and operates with the high temperature cooler at a temperature in the approximate range of 60 to 100 F. and with the temperature of tube 24 being approximately -30 F.

The second or low temperature system consists of a compressor so driven by the electric motor 32. The discharge pipe 34 of this compressor is in communication with the interior of the heat exchanger 26. The liquid refrigerant collecting at the bottom of this heat exchanger is discharged through pipes 36 and 36a and dehydrator 38 to the reservoir 41). The discharge passage of the reservoir 4% is a beveled valve seat opening b in the pipe 42 leading to the low temperature evaporator 44, the outlet of which is connected to the intake of the compressor 3%}. in this system, which may, for example, be charged with a refrigerant such as Freon 13, Freon 22, or the refrigerant marketed by the Minnesota Mining and Manufacturing Company as Kulene, the heat exchanger 26 cools the compressed refrigerant to the approximate temperature of the evaporating refrigerant in the tube 24. The cooled liquid refrigerant then passes to the reservoir 40 and to the line 42 to the low temperaure evaporator 44 where it evaporates to produce the low temperature which may, for example be l40 F.

The flow of low temperature refrigerant to the line 42 is controlled by the float valve mechanism indicated generally at 48. This mechanism consists of a pivotally supported arm 54) having a pendulus, conical closure member 52 which seats on the mating beveled face of the valve seat 49b which is formed at the opening of passage 40a. A ball float 54 is affixed to the outboard free end of the arm 56. When the liquid level in the reservoir iii falis below a predetermined point, the float 54 descends sufficiently to cause the closure member 52 to seat on the valve seat 40b and thereby block passage of refrigerant to the pipe 42. On the other hand, when the liquid level rises above this cut-off level, the float 52 ascends to lift the arm 50 and the closure member 52 to allow flow of refrigerant from the reservoir to the pipe 42 and hence evaporator 4-4.

The float valve 48 meters the discharge of refrigerant from the reservoir ill to prevent exhaustion of the refrigerant from the reservoir and the heat exchanger 26. However, when the unit is started from a heated condition and the heat exchanger 26 brought down to operating temperature the float 48 may be held shut even though liquid in the reservoir 40 exceeds the level at which the closure 52 unseats. This is due to the buildup of gas pressure in the upper part of the reservoir 44). Such pressure can be. quite great since the reservoir 40 is not cooled by the heat exchanger 26 and thus boils some of the refrigerant until the equilibrium pressure for that high temperature is reached.

In accordance with the present invention the gas pressure above described is relieved by providing a discharge path for vapor flow'from the-reservoir40 to the interior of heat exchanger 26. This path is formed by the pipe 56 which is connected at its lower-end to outlet passage 40c of the reservoir 40 and at its upper end to the top-'part or dome 57 of the heat exchanger 26. If the reservoir 40 isinitially at a high temperature, and the refrigerant boils therein because of that temperature, the vapor passes from the reservoir 4%) back through pipe 56 into the heat exchanger 26 and does not build up pressure. The reservoir 40 then is cooled by the boiling refrigerant to'operating temperature and the valve closure 52 lifted when the liquid refrigerant exceeds the preset level.

The-low temperature operating motor 32 is energized through 'a low-temperature'cut-out 62 and a high pressure cut-out'64. These are connected in series circuit with the motor so that opening of-either deenergizes the motor. The low temperature cut-out 62 may be any one of many welliknown switches responsive to the pressure or the temperature of the low temperature evaporator 44 and operable, when a predetermined low temperature or pressure is reached, to open switch elements to interrupt the current supply to the motor 32. The high pressure cut-out may likewise be ony one of many well known switches responsive to the pressure or the temperature in the heat ex changer 26. When that pressure or temperature exceeds a predetermined safe value, the cut-out opens circuit elements to interrupt the energizing circuit to the motor 32.

When the entire unit is started from the shutdown conditionat room temperature, the high pressure cut-out 64 prevents operation of motor 32 until a safe temperature exists within the heat exchanger 26. When that temperature is reached, the motor 32 is energized since the low temperature cut-out calls for refrigeration. When the compressor 30 builds up a suflicient supply of liquid refrigerant in reservoir 40, the valve 43 lifts to discharge refrigerant-to the evaporator 44. Since the pressurewithin the reservoir 40 is relieved by the pipe 56, that valve lifts when the requisite fluid level builds up and is not delayed or blocked by pressure buildup within the reservoir. Refrigeration action is then produced by evaporation in the evaporator 4. The motor 32 is then intermittentlyenergized by the low temperature cut-out 62 as required to maintain the preset regulated low temperature.

The high temperature system may have any one of many suitable operating controls. Such controls may include a low temperature cut-out (not shown) sensitive to the pressure or the temperature in the tube 24 and operable to interrupt the energizing circuit to motor 12 when the temperature falls below a fixed value. In addition, the expansion valve 2!} may be controlled in response to the temperature in the tube 24, this being achieved by a suitable bulb 58 positioned in tube 24 and connected to pipe 60. Thermally expansible fiuid is placed in'the bulb 58 and the pipe 60 and expands as the temperature of bulb 58 rises to increase the flow through expansion valve by suitable means (not shown).

The high temperature cooler 16 is a heat exchanger which may be any one of many types well known in the art. In most applications this cooler takes the form of'a radiator having a serpentine copper pipe with fins through which the refrigerant travels. Air is blown over the pipe and fins to cool the same.

The low temperature evaporator 44 is in the space to be cooled. It may be any one of many types well-known in the art. Typically, it consists of a coil of copper tubing located within the space to be cooledto define a heat exchanger. It may, if desired, have heat conducting fins.

In the modified form of the invention shown in Figure 2,the 'heat exchanger 26'has a-Well 126 defined 'by'the depending pipe 140 and the'bottom closure plate 141. The liquid refrigerant flows directly into this well rather than through the pipes 36 and 36a and dehydrator 38 as in Figure l. -Abottomoutlet-passage 149a is provided in plate 141 and is COIlIlECtCdrtO the pipe 42 leading to the low temperature evaporator (Figure 1). A float valve 148 using ball float 154, arm 150, and closure 152 is provided as in the case of reservoir 4-0, Figure 1, to close the passage a when the level of the liquid refrigerant in the Well 126 falls below a predetermined point.

The closure plate -141 is secured in position by the bolts 141a whichareeach'thread'cdly received by a threaded hole in-the flange'140bWhichis welded to the free end of the-pipe140 as shown.

In the embodiment of Figure 2, the well126 defined by pipe -140is-in direct communication with the interior of the heat exchanger/26. This affords a passage for vaporized refrigerant from the reservoir formed by the well to the heat exchanger and thus prevents buildup of gas pressure in the well in excess of the gas pressure in the heat exchanger 26.

Apparatus constructed-in accordance with the present invention should be provided with heat insulation to prevent loss of cooling effect and the deposit of frost on the apparatus. Such insulation (not shown in the drawings) .should jacket the coldparts of the apparatus and may be anyone of many types well known in the art.

'In the claims, I have referred to the tube 24 as the evaporator .of the high temperature system and the interior fot the heat exchanger 26 as the cooler of the low temperature system. Since the tube 24 is within the exchanger 26, these parts are in good thermal contact andare in good heat-exchange relation.

-While I have shown and described specific embodiments of the present invention, it will be understood thatvariousialternativearrangements may be made without departing from the true spirit and scope of the invention. I, therefore,-intend'by the appended claims to cover all modifications and alternative constructions falling withintheir true spirit and scope.

I claim:

1. A low temperature refrigeration apparatus for use in cascade'with a high temperature refrigerating system, the latterrhaving a pump, cooler, and evaporator and in which refrigerant'is pumped from the evaporator to the cooler; said low temperature refrigeration apparatus comprising a pump, cooler and evaporator, and operable to .pump refrigerant from said last evaporator to said last cooler, said cooler of said low temperature apparatus comprising a compartment, the interior of which is in heat exchange relation with the evaporator of the high temperaturesystem; said last pump being outside said compartment; a reservoirin said low temperature apparatus positioned to receive liquid refrigerant from said low temperature co'oler and having an outlet at its lower p0rtion communicating withsaid low temperature evaporator; a float valve in said reservoir operable to close the outlet when the liquid level in said reservoir falls below a predetermined point, and means defining a path for gas flow from the upper part of said reservoir to said low temperature cooler.

2. A low temperature refrigeration apparatus for use in cascade with a high temperature system, the latter having a pump, cooler, and evaporator and in which refrigerant ispumped from the evaporator to the cooler; saidlow temperature refrigeration apparatus comprising a pump, cooler and evaporator, and operable to pump refrigerant from said last evaporator to said last cooler, said cooler'of said low temperature apparatus comprising acompartment having its interior in heat exchange relation' with the evaporator of the high temperature system; said last pump being outside said compartment; a reservoirymeans defining a-passage for liquid refrigerant from said low temperature'cooler to said reservoir; means defining a passage for liquid refrigerant from the bottom of said reservoir to .said low temperature evaporator; a

float valve mechanism in said reservoir and operable to close the outlet passage from the same when the liquid level in said reservoir falls below a predetermined point; and means defining a passage for vapor flow from the top of said reservoir to the top of said low temperature cooler.

3. A loW temperature refrigeration system for use in cascade with a high temperature system, the latter having a pump, cooler, and evaporator and in which refrigerant is pumped from the evaporator to the cooler; said low temperature refrigeration system comprising a pump, cooler and evaporator, and operable to pump refrigerant from said last evaporator to said last cooler, said cooler of said low temperature system being in heat exchange relation to the evaporator of the high tempera- 1) ture system, said cooler of said low temperature system comprising a compartment having a Well said pump of said low temperature refrigeration system being located outside of said compartment; means defining a liquid passage from the bottom of said well to said low temperature evaporator; and a float valve mechanism in said Well operable to close said passage when the liquid level in said Well falls below a predetermined point.

References Cited in the file of this patent UNITED STATES PATENTS 2,047,753 Stiening July 14, 1936 2,145,692 Jones Jan. 31, 1939 2,274,391 Zwickl Feb. 24, 1942 2,319,502 Gould May 18, 1943 2,463,671 Bach Mar. 8, 1949 

